Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3


Please don’t jump to conclusions; MTH did NOT manufacture the C&O 2-6-6-6 Allegheny with MTH Proto-Sound 2.0 (PS2.0) I found on eBay. Instead, it’s a brass locomotive produced by Sunset 3rd Rail (Figure 1) and converted to PS2.0 (see MTH PS2.0 Upgrade Manual). See Figure 2. The retrofit replaced the original tender QSI-OEM Digital Soundboards, the wiring harnesses for the tender and locomotive, and the Suethe smoke units and their voltage regulator board in the locomotive.

Figure 1: Sunset 3rd Rail C&O Allegheny box info


Figure 2: Original tender Proto-Sound 2.0 electronics and harness wiring

It was a well-done conversion, so I was very reluctant to tear out the tender PS2.0 control board and the wiring harnesses in the tender and locomotive. The PS2.0 conversion used an MTH smoke unit with fan speed and smoke intensity controls.

Figure 3: MTH Smoke Unit with funnel

The CVP Airwire receiver boards I typically use for dead-rail conversion don’t have this level of smoke unit control. And the PS2.0 board used a speed encoder on the locomotive motor’s flywheel to synchronize the PS2.0 board’s sound. See Figure 5 for the speed encoder reader and flywheel strip and 5b for additional electrical connections.

Figure 4: Original Constant Voltage Unit wiring with dead-rail modifications indicated


Figure 5: Speed encoder, flywheel strip, and electrical connections for the Constant Voltage Unit.


Figure 5b: Locomotive harness wiring after modifications connecting the Constant Voltage Source to Battery +/- and replacing incandescent bulbs with LEDs

These built-in features were excellent, but I still wanted a dead-rail conversion.

Hmm… Looking around, I discovered that Proto-Sound 3.0 (PS3.0) had DCC/DCS control options, and the wiring harnesses are the same for PS2.0 and PS3.0 boards (see, for instance, MTH PS3.0 Upgrade Manual). Things are looking up. Then I found a great site, Ray’s Electric Trainworks, that provides PS3.0 replacement boards and great support.

My thought was this: if I can upgrade the locomotive to PS3.0, then I can take the following steps. Jumper the PS3.0 board to DCC operation, disconnect the original rail power/communication wiring, and re-connect the rail power/communication wiring to the DCC outputs of a CVP Airwire CONVRTR-60X receiver (CONVRTR Users Guide). Easy, right? Not so fast.

Ray at Ray’s Electric Trainworks was a great help: he steered me to the right PS3.0 card I needed for the tender and loaded the Allegheny sound file for me. Otherwise, I would need a bunch of DCS infrastructure to load the sound file. And he gave me a rebate for the old PS2.0 card! Great guy.

OK, I have the PS3.0 card from Ray. The PS3.0 card came mounted in its plastic carriage that is screw-mounts on the tender chassis through pre-existing holes. The heatsink orients a bit differently between the PS2.0 and PS3.0 – no big deal – I just needed to drill a hole in the tender chassis in a slightly different place. The PS3.0 doesn’t use a Ni-MH battery, so out it went. That was a good thing, too, since I needed the real estate for the replacement LiPO battery to supply power to the control boards, lights, smoke unit, and locomotive.

Locomotive Modifications

Here is a diagram of the locomotive wiring harness from the MTH PS3.0 Upgrade Manual with my annotations.

Figure 6: Locomotive PS3.0 wiring harness with modifications indicated

Since I wouldn’t send track power to the tender, I cut the Ground Lead and Pickup Roller Leads wires. I re-purposed them by connecting these harness wires to the Constant Voltage Unit, a heat-shrink blob whose input leads were cut from their original chassis connections (see Figure 5 again).

While I was at it, I removed the incandescent cabin and headlight bulbs to reduce power consumption. I replaced them with Yeloglo LEDs (see Yeloglo description), whose + input was in series with the Yeloglo’s 470-ohm resistor for 10-16 Volt operation. Yeloglo LEDs have an excellent yellowish output reminiscent of incandescent light.

Tender Modifications

The diagram below shows the tender’s wiring harness with my modifications.

Figure 7: Tender PS3.0 wiring harness with modifications indicated

Continuity testing revealed that the locomotive Roller Pickup Leads and the Ground Lead connected to Pin 1 and 3 of the 7-pin connector, respectively.

Note that BOTH locomotive and tender Ground Leads (both are black) that are input to the PS3.0 on pins 3 and 4 of the 7-pin connector, respectively, MUST BE DISCONNECTED FROM THE LOCO/TENDER FRAMES AND CONNECTED to the “B” DCC output of the CONVRTR. This pair of connections was the trick. I initially connected ONLY the Ground Lead from the locomotive (pin 3 of the 7-pin connector) to the CONVRTR, which did NOT work! I don’t know if only connecting pin 4 of the 7-pin connector would work – I didn’t try it.

Similarly, I disconnected the red wire that is input to the PS3.0 on pin 1 of the 7-pin connector (which initially connected to the locomotive Roller Pickup Leads) from the plug bundle that connects the tender to the locomotive. I connected it to the “A” output of the CONVRTR.

The “harness side” of the two cut wires originally going to the Pickup Roller Leads (red) and Ground Lead (black) on the locomotive were connected to switched Battery + and Battery – (ground), respectively, to provide power to the locomotive’s Constant Power Unit.

Note: “Switched B+” means battery power coming from the Battery’s + terminal that is turned on or off with a switch (you want to be able to turn off the power!). “Battery – (ground)” means the connection to the Battery’s negative terminal that is usually grounded to the tender chassis by a battery charging plug.

A picture is worth a thousand words, so studying Figures 6 and 7 will tell you what wiring cuts and re-connections are needed to convert a Proto-Sound 3.0 steam locomotive to dead-rail.

Other Dead-Rail Conversion Details

Of course, other aspects of the dead-rail conversion are required. These aspects include adding battery power and CONVRTR connections and removing center-rail pick-ups and electrical connections that are part of a typical 3-rail to dead-rail conversion for an O-scale steam locomotive. These conversion aspects are discussed in another blog.


In summary, if you have a locomotive with the PS3.0 installed, conversion to battery-powered DCC operation and radio control (dead-rail) is straightforward once you know the few wiring cuts and re-connections you need to make. The DCC operations for this particular locomotive can be found in the MTH document “Premier 2-6-6-6 Allegheny Steam Engine .” What you preserve with the PS3.0 is good DCC functionality, the original sound, and coordinated smoke – and that’s a pretty nice combination.

Author: Darrell Lamm

I earned my Doctorate in Physics from the Georgia Institute of Technology in 1982, and before retiring in 2019 I worked for 37 years at the Georgia Tech Research Institute. My last position was Chief Scientist of the Electro-Optical Systems Laboratory. Like many people, my love for model railroading began at an early age, and I rekindled that interest starting in 2017.

10 thoughts on “Dead-Rail Conversion of a Sunset 3rd Rail Allegheny 2-6-6-6 Locomotive with MTH Proto-Sound 3”

  1. Glad you stopped by. I have another post on converting an MTH 2-8-8-8-2 Virginian Triplex to dead-rail using a Proto-Sound 3.0 board operating in DCC mode. Please check it out to gain a deeper understanding of converting locomotives equipped with Proto-Sound 3.0 to dead-rail.

    In general, locomotives equipped with Proto-Sound 3.0 are easy to convert to dead-rail because all of the DCC control of the motor and accessories, such as lights and smoke units, are already interfaced with the PS 3.0. Conversion is quite easy – almost a joy. Having dealt with interfacing fan-driven smoke units to onboard DCC decoders, the PS 3.0 eliminates the hassle.

  2. I just read your triplex article. Very interesting. I have a ps 2 0-8-0 that I would like to convert. I do not have a dcc system though. Also no DCS controller either. How would you recommend I get started?

    1. Hi Phil! Glad you got something out of the post. I am assuming you want to convert to “dead-rail.” There are many ways you can go. If I were in your shoes, I would first buy a PS 3 board from Ray’s Electric Trains. The Triplex blog proves a link to Ray’s website. He may even give you a refund for your old PS 2 board. Ray will work with you, and part of the fun of this hobby is meeting and working with great people. Since the PS3 board is either DCC or DCS, you can use either “system,” and you will probably be able to retain the sound and other features that MTH provided.

      For the “dead-rail” aspect, as the blog describes for the triplex
      – disconnect the pick-up shoes,
      – disconnect the outside and inside rail connections to the PS3 board (there is probably no need to cut any rail power connections in the locomotive),
      – connect the DCC output from the wireless receiver board to the PS3 board,
      – set the PS3 jumper to DCC, and finally
      – connect the wireless receiver to batteries and an external antenna

      As for the selection of batteries and wireless receivers/throttles, there are several sites that provide information and products. The best sites that come to mind are and CVP Airwire. They can both steer you to DCC-compatible wireless solutions that operate in the 915MHz “ISM” (largely unregulated in the US) band. You can also use a “Bluerail” solution that operates using Bluetooth, which means you can connect to the onboard receiver using your smartphone. See link for further details.

      I hope this jumpstarts you. There is also a Facebook group on dead-rail that you might want to join.

      1. Darrell,

        Thanks for the reply. Also thank you for putting all this information down in this blog for the rest of us like my self that are not as well versed in electronics. It is much appreciated.

        In regards to Dead Rail. For years I have leaned more towards just regular radio control. This is because I have had little exposure to DCC. Also I always saw it as an added expense. A large on in some cases. I did one engine as a temporary experiment using a stripped out MTH Railking 2-8-0. Not a scale engine but it was cheap $20.00. This was 11 years ago and I used an old 27mghz rc car take off equipment. It worked ok. I also have some newer 2.4 gig stuff I plan to use now but have not yet. On the engine I mentioned that is PS2 MTH. I would like to retain the sound as I have never had a loco with that. So I will look into the method you lay out converting to PS3 etc.. for that one. I am also a scale modeler So I will look into re profiling the wheels. Originally I was going to convert this loco to track power 2 rail. It will be easier to just cut down the flanges as you have done and leave the tires wide. This does not bother me. I will be running on my own out door layout as well as a traction layout that has both rails common with the power on the over head. An RC loco will be great for switching on this layout. While trolleys run on the loop line.

        Thanks for the invite to the FB group. I have been a member of it for some time.

        1. Thanks again, Phil. I should have checked the rolls on the Facebook dead-rail group before suggesting it to you. I’m not sure I understand your comments about power on the traction layout, but if you convert any 3-rail locomotive to dead-rail, remember that both the locomotive’s and tender’s wheels short across both rails. I am investigating techniques for applying a very tough insulating coating on all the wheels on one side to prevent the possibility of shorting across the tracks should you try to use a converted 3-rail locomotive on powered two-rail trackage.

  3. Darrell,
    Hi again. What I was talking about on the traction layout is that it is essentially a 3 rail layout with the over head wire being the third rail and the two rails of the track being common same polarity and the wire being the other polarity. So you don’t need insulated wheels to run if you are running an RC engine like I want too. On the other two rail layout I run on yes your point is well taken that I would need two rail insulation as we run that layout on two rail DC.

    1. Thanks for the interest and feedback. Do you have dead-rail experience? I will be in contact for those additional decoders is a couple of weeks.

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